1. Technical Field
The present invention relates to a device for filtering a fluid contaminated with particles. More specifically, but without restriction to the particular embodiment and/or use which is shown and described for purposes of illustration, the present invention relates to a device for filtering a fluid contaminated with particles used on an exhaust gas transporting particulate matter from an engine.
2. Discussion
Filter devices of porous materials are generally known, these filter devices usually being arranged in an outside container. Serving here as the material for the filter devices is generally a porous material which may be, for example, a sintered material composed of metallic materials or else of glass or plastics.
Particularly when they are intended as particulate filters for engine exhaust systems, the filter devices are usually made up of filter plates of the porous material mentioned above lying one behind the other in an outer container.
When the filter devices are used as a particulate filter for the exhaust gases of an engine, the filter device and silencer in the exhaust line of the engine are often combined to form one unit.
With this customary construction of the filter stems, the fluid to be filtered must penetrate one or more layers of the porous material to achieve an adequate cleaning effect. Due to the large surface areas of porous material required, this results in multi-layered filters which oppose the flowing fluid with a very high flow resistance.
Alternatives to this are to produce the particle filters from metal meshes or roughened aluminium-oxide yarn.
U.S. Pat. No. 2,926,743 discloses a free-flow silencer for an exhaust system which comprises two tube elements lying one inside the other, the inner one of the tube elements having a cross-sectionally star-shaped form, which opens out into the outer tube with a terminating element in the manner of a Venturi nozzle. This free-flow silencer is capable of cooling the exhaust gases, reducing their flow velocity and effectively avoiding their pressure fluctuations. As a result, very efficient cooling and silencing of the exhaust gases in the exhaust system is achieved.
Accordingly, it is the object of the invention to provide a device for filtering a fluid contaminated with particles, in particular an exhaust gas transporting particulate matter from an engine, which device has a large surface area of porous filter material, with ideal space utilization in a prescribed outer container, and which also helps to reduce sound waves and pressure fluctuations in the fluid.
The actual filter unit in the outer container is formed according to the invention by a porous material that extends in the direction of flow being repeatedly folded along this direction of flow and joined together by the free ends, so as to produce a cross-sectionally closed geometrical form which has at least one inner opening. The material may thus be folded, for example, in the manner of a multi-pointed star, so that a kind of tube with a star-shaped cross section is produced from the porous material.
The fluid to be filtered then penetrates this star-like structure from inside to outside or from outside to inside, by the fluid either being introduced into the porous material and flowing from there into the region of the outer container or by the fluid being allowed into the outer container and then drawn out of the least one internal opening in the cross section of the porous material.
The folds make it possible, according to their number, to accommodate a quantity of surface area that is adapted in the best way possible to requirements, or is as great as possible, in the outer container, the geometrical dimensions of which are usually prescribed.
The fact that only the number and form of the folds has to be changed allows the respectively required filter device to be produced from an endless strip of the porous material. Since this device is usually produced by numerically controlled machines, it is sufficient here to store for the respectively required filter device a slightly amended control program, which can produce the filter device adapted to the respective requirements from the same material in each case, without necessitating great readjustments on the machine.
In a particularly favourable embodiment of the invention, the outer container with the filter device serves not only for filtering an exhaust gas contaminated with particles but at the same time as a silencer. This means that any pressure waves there may be in the exhaust gases are reduced by the unit comprising the outer container and filter device, so that no disturbing noises can be emitted to the area surrounding the system. The great porous surface area is also almost ideal for this, since it makes possible corresponding acoustic effects which allow the sound waves in the exhaust gas to xe2x80x9crun their coursexe2x80x9d.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from a reading of the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.